Flights could only day be free. Is it ever going to happen and how could it work.
Free flights would work in the way that any current free services work. The flight itself would be free, but you'd have to pay all necessary taxes, credit card charges and luggage costs. There would probably be a number of others fees to ensure that you don't take flights from Milwaukee to Phoenix and appear on the other side no lighter in your pocket. These flight will one day in the future make money by charging for various different services.
For example on a long flight like flights from New York to Puerto Vallarta you may find that to get a seat that folds down into a bed you'll need to pay an extra fee. And if you want to eat a meal, which you'll more likely want to do, you'll need to pay a fee. There will also be other things that could be purchased, for example a spa treatment while on the flight. There could also be sponsorship of the flights and adverts displayed all throughout the flight.
You shouldn't expect that flights from Detroit to Nassau to be free anytime soon, but some European countries already have flights are technically free, but only when booked along with a return flight that costs the sort of price that you might imagine air travel would cost. So free flights are a distant dream and the only real free flights will be the one taken by businessmen who have their employer pay the bill for the flight, or for competition winners. Everyone else will need to paying full price for the time being. Free flights are a distant dream, and they are unlikely to be so 'free' after all in all likelihood.